Much research regarding batteries as a power source has been conducted to minimize the requisite number or size of batteries for portable electronic devices such as video cameras, cellular phones and laptop computers. In particular, rechargeable lithium batteries have around three times the energy density per unit weight of conventional storage batteries such as lead-acid batteries, nickel-cadmium batteries, nickel-hydro batteries and nickel-zinc batteries. In addition, rechargeable lithium batteries can be recharged relatively quickly.